U.S. patent number 7,930,373 [Application Number 12/165,564] was granted by the patent office on 2011-04-19 for system and method for controlling a phy attached to a mac interface for energy efficient ethernet.
This patent grant is currently assigned to Broadcom Corporation. Invention is credited to Wael William Diab.
United States Patent |
7,930,373 |
Diab |
April 19, 2011 |
System and method for controlling a PHY attached to a MAC interface
for energy efficient ethernet
Abstract
A system and method for controlling a physical layer device
attached to a media access control interface for energy efficient
Ethernet. Detecting of a condition that is conducive to a change in
a link rate can be performed at either link partner. In one
embodiment, a control message based on the detection can be sent to
a physical layer device via a media access control layer interface
to effect a link rate change in the physical layer device.
Inventors: |
Diab; Wael William (San
Francisco, CA) |
Assignee: |
Broadcom Corporation (Irvine,
CA)
|
Family
ID: |
41448871 |
Appl.
No.: |
12/165,564 |
Filed: |
June 30, 2008 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20090327506 A1 |
Dec 31, 2009 |
|
Current U.S.
Class: |
709/220;
709/221 |
Current CPC
Class: |
H04L
47/10 (20130101); H04L 47/13 (20130101); H04L
47/25 (20130101); H04L 47/30 (20130101); Y02D
30/32 (20180101); Y02D 30/00 (20180101) |
Current International
Class: |
G06F
15/177 (20060101) |
Field of
Search: |
;709/220,221 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lin; Kenny S
Attorney, Agent or Firm: Kobayashi; Duane S.
Claims
What is claimed is:
1. An energy efficient Ethernet method, comprising: detecting a
condition that is conducive to a change in a link rate of an
Ethernet link; sending a message to a media access control layer
that identifies a change to a link rate of said Ethernet link;
changing a rate of operation of said media access control layer
after receipt of said message; signaling, by said media access
control layer to a physical layer device, an instruction to change
said link rate of said physical layer device; and changing an
operating state of said physical layer device upon receipt of said
instruction.
2. The method of claim 1, wherein said detecting comprises
monitoring a buffer or queue.
3. The method of claim 1, wherein said detecting comprises
monitoring a subsystem state.
4. The method of claim 1, wherein said signaling is done in
band.
5. The method of claim 1, wherein said signaling is done out of
band.
6. The method of claim 1, wherein said changing an operating state
comprises switching to a subset physical layer device.
7. The method of claim 1, wherein said changing an operating state
comprises switching to a low power idle mode.
8. The method of claim 1, wherein said changing an operating state
comprises switching from a subset physical layer device to a parent
physical layer device.
9. The method of claim 1, wherein said changing an operating state
comprises switching from a low power idle mode to an active
mode.
10. The method of claim 1, wherein said changing a rate of
operation of said media access control layer comprises changing a
rate of operation of an interface with said physical layer
device.
11. An energy efficient Ethernet method in a physical layer device,
comprising: receiving a link utilization change message via an
interface that couples the physical layer device to a media access
control layer; switching from a first link rate to a second link
rate in response to a receipt of said link utilization change
message, wherein one of said first link rate and said second link
rate is lower than the other link rate; and switching a part of
said media access control layer that supports said interface from a
first rate to a second rate in response to a condition that
produces said link utilization change message.
12. The method of claim 11, wherein said receiving comprises
receiving via in band signaling on said interface.
13. The method of claim 11, wherein said receiving comprises
receiving via out of band signaling on said interface.
14. An energy efficient Ethernet method, comprising: detecting,
using components in a layer above a media access control layer, a
condition that is conducive to a change in a link rate of an
Ethernet link; sending, in response to said detection, a message to
said media access control layer that indicates a change a link rate
of said Ethernet link; signaling, by said media access control
layer to a physical layer device, an instruction to change said
link rate of said physical layer device; changing, in response to
said message, an operating state of a part of said media access
control layer that supports an interface between said media access
control layer and said physical layer device; and changing an
operating state of said physical layer device upon receipt of said
instruction from said media access control layer.
15. The method of claim 14, wherein said detecting comprises
monitoring a subsystem status.
16. The method of claim 14, wherein said detecting comprises
monitoring in an application layer.
17. The method of claim 14, wherein said detecting comprises
monitoring a bandwidth allocation protocol.
18. The method of claim 14, wherein said changing an operating
state of said physical layer device comprises changing to a subset
mode of operation.
19. The method of claim 14, wherein said changing an operating
state of said physical layer device comprises changing to a low
power idle mode of operation.
20. The method of claim 14, wherein said signaling comprises
signaling using in band communication on said interface.
21. The method of claim 14, wherein said signaling comprises
signaling using out of band communication on said interface.
Description
BACKGROUND
1. Field of the Invention
The present invention relates generally to Ethernet systems and,
more particularly, to a system and method for controlling a
physical layer device attached to a media access control interface
for energy efficient Ethernet.
2. Introduction
Energy costs continue to escalate in a trend that has accelerated
in recent years. Such being the case, various industries have
become increasingly sensitive to the impact of those rising costs.
One area that has drawn increasing scrutiny is the IT
infrastructure. Many companies are now looking at their IT systems'
power usage to determine whether the energy costs can be reduced.
For this reason, an industry focus on energy efficient networks has
arisen to address the rising costs of IT equipment usage as a whole
(i.e., PCs, displays, printers, servers, network equipment,
etc.).
One area that has shown the potential for cost and energy savings
is efficient link utilization. Most network links are typically in
an idle state between sporadic bursts of data. The overall link
utilization is therefore relatively low. In one solution, the link
rate can be reduced when the high data capacity is not needed,
thereby saving energy. In other words, a link can use a high data
rate when data transmission needs are high, and use a low data rate
when data transmission needs are low. In another solution, a link
can be designed to enter into a low power idle mode where the
active channel is turned silent. While these solutions can provide
significant energy savings, what is needed is a mechanism for
controlling physical layer devices that implement efficient link
utilization.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to describe the manner in which the above-recited and
other advantages and features of the invention can be obtained, a
more particular description of the invention briefly described
above will be rendered by reference to specific embodiments thereof
which are illustrated in the appended drawings. Understanding that
these drawings depict only typical embodiments of the invention and
are not therefore to be considered limiting of its scope, the
invention will be described and explained with additional
specificity and detail through the use of the accompanying drawings
in which:
FIG. 1 illustrates various layers and their relation to the ISO
Open System Interconnection (OSI) reference model.
FIG. 2 illustrates an example of a coordinated end-to-end control
policy.
FIG. 3 illustrates an example of a controller.
FIG. 4 illustrates an example of a switch.
FIG. 5 illustrates an example of a power consumption mode
determination.
FIG. 6 illustrates an example of a power consumption mode
determination using a transmit queue.
FIG. 7 illustrates a flowchart of a control process of the present
invention.
FIG. 8 illustrates a flowchart of a symmetric operation of the
present invention.
FIG. 9 illustrates an embodiment of a physical layer device having
a multi-packet buffer.
SUMMARY
A system and/or method for controlling a physical layer device
attached to a media access control interface for energy efficient
Ethernet, substantially as shown in and/or described in connection
with at least one of the figures, as set forth more completely in
the claims.
DETAILED DESCRIPTION
Various embodiments of the invention are discussed in detail below.
While specific implementations are discussed, it should be
understood that this is done for illustration purposes only. A
person skilled in the relevant art will recognize that other
components and configurations may be used without parting from the
spirit and scope of the invention.
Ethernet has become an increasingly pervasive technology that has
been applied in various contexts such as twisted pair and
backplane. IEEE 802.3az Energy Efficient Ethernet (EEE) continues
to evaluate various methods for reducing energy used by reducing
link rates during periods of low link utilization. In this process,
a protocol would be defined that would facilitate transition to and
from lower power consumption modes in response to changes in
network demand.
One of the protocols being considered is a subset PHY technique. In
this subset PHY technique, a low link utilization period can be
accommodated by transitioning the PHY to a lower link rate that is
enabled by a subset of the parent PHY. In one embodiment, the
subset PHY technique is enabled by turning off portions of the
parent PHY to enable operation at a lower or subset rate. For
example, a subset 1G PHY can be created from a parent 10GBASE-T PHY
by a process that turns off three of the four channels. In another
embodiment, the subset PHY technique is enabled by slowing down the
clock rate of a parent PHY. For example, a parent PHY having an
enhanced core that can be slowed down and sped up by a frequency
multiple can be slowed down by a factor of 10 during low link
utilization, then sped up by a factor of 10 when a burst of data is
received. In this example of a factor of 10, a 10G enhanced core
can be transitioned down to a 1G link rate when idle, and sped back
up to a 10G link rate when data is to be transmitted. Another of
the protocols being considered is low power idle (LPI). In general,
LPI relies on turning the active channel silent when there is
nothing to transmit. Energy is thereby saved when the link is off.
In general, both the subset and LPI techniques involve turning off
portions of the PHY or otherwise modifying the PHY during periods
of low link utilization.
Regardless of the method by which one or more low power consumption
modes is implemented by the PHY, control of such transitions is a
key factor. In one example, the control and operation of the
transition between different power consumption modes is confined to
the PHY itself. Here, the PHY can examine the relative amount of
traffic that is transmitted to allow for a current link utilization
analysis. This link utilization analysis can then be used by the
PHY in deciding whether to change a power consumption mode, for
example, by reducing a link rate or entering a low power idle
mode.
Isolation of this transition process in the PHY has some
disadvantages. For example, the PHY can only analyze current
traffic transmission levels. It would not have any insight into
other traffic-related factors (e.g., buffers, queues, subsystem
status, etc.) in higher layers. Additionally, the isolation of the
transition process in the PHY would not enable power savings to be
realized in other higher layers, such as the media access control
(MAC) layer.
It is therefore a feature of the present invention that control of
the power consumption mode transition process can be effected at
layers above the PHY. To illustrate the principles of the present
invention, reference is first made to FIG. 1, which illustrates the
various layers and their relation to the ISO Open System
Interconnection (OSI) reference model.
As illustrated, the physical layer includes a physical coding
sublayer (PCS), a physical medium attachment (PMA), and physical
media dependent (PMD). The PCS is coupled to a reconciliation
sublayer (RS), which provides a signal mapping between interface
110 and the MAC layer. In various examples, interface 110 can be
based on an Attachment Unit Interface (AUI), media independent
interface (MII), serial MII (SMII), reduced MII, (RMII), gigabit
MII (GMII), reduced GMII (RGMII), serial GMII (SGMII), 10 gigabit
MII (XGMII), 10-Gbps AUI (XAUI), or the like. In a GMII example,
the PCS is generally responsible for encoding/decoding GMII octets
to/from ten-bit code-groups (8B/10B) for communication with the
underlying PMA. In an XGMII example, the PCS is generally
responsible for encoding/decoding XGMII 64-bit data to/from 66-bit
code-groups (64B/66B) for communication with the underlying
PMA.
In general, the PMA abstracts the PCS from the physical medium.
Accordingly, the PCS can be unaware of the type of medium. The
primary functions of the PMA include mapping of transmit and
receive code-groups between the PCS and PMA,
serialization/de-serialization of code-groups for
transmission/reception on the underlying PMD, recovery of clock
from the coded data (e.g., 8B/10B, 64B/66B, etc.) supplied by the
PMD, and mapping of transmit and receive bits between the PMA and
PMD.
The PMD is generally responsible for generating electrical or
optical signals depending on the nature of the physical medium
connected. PMD signals are sent to the medium dependent interface
(MDI), which is the actual medium connected, including connectors,
for the various media supported.
As noted, one of the ways of creating an energy efficient network
is through efficient link utilization. In general, the lack of data
transmission does not significantly reduce energy consumption of a
PHY in most implementations. A 10 Gbit/s link, for example, will
consume about the same amount of power whether a burst of data is
transmitted during a file transfer, a constant stream of data is
transmitted at lower bandwidth, or no data is transmitted during an
idle period. If a 10 Gbit/s link can be turned off or slowed down
(e.g., to a 1 Gbit/s link) during idle times, then power can be
saved in the operation of the PHY.
In accordance with the present invention, control of the power
consumption mode transition process can be effected outside of the
PHY. In one embodiment, the control policy can be effected in the
MAC, MAC control, MAC client, or higher layers such as the
application layer.
FIG. 2 illustrates an example of a coordinated control policy that
can be used to impact the operation of a PHY. In general, energy
efficient Ethernet mechanisms can touch a number of devices and
software throughout the stack and across the link. In the example
illustration of a link between a server and a switch, energy
savings are sought to be effected in the link between the PHYs in
the server and the switch. The control policy that governs the
operation of the link between the PHYs can be implemented in one or
more layers above the PHY in the server and/or switch. As would be
appreciated, the particular mechanism by which the control policy
is effected would be implementation dependent. The key, however, is
the linkage of the control policy to the EEE savings that can be
produced in transitioning the operation of the PHYs. In one
example, a coordinated control policy can include the exchange of
load information by the two ends of the link ahead of time. FIG. 3
illustrates an example controller system in which the principles of
the present invention can be implemented. In various examples, the
controller can be part of a client (e.g., laptop, desktop or
workstation), a server (e.g., audio-video (AV) server, high
performance computing (HPC) server), or a consumer edge device
(e.g., HDTV, Blueray, etc.). As illustrated, host system 330 is
coupled to integrated Ethernet controller 310 via interface 320.
Ethernet controller 310 further includes PHY 311, which is coupled
to MAC 313, via interface 312 such as that described above with
reference to FIG. 1. In the illustrated example, MAC 313 is coupled
to PCI Express device 317 via memory controller 314, which is also
coupled to buffers 315 and processor 316.
In this example system, host 330, processor 316, and/or MAC 313 can
be designed to monitor one or more conditions to determine whether
a transition in a power consumption mode should be made. In one
example, the monitoring is of a buffer level relative to a
watermark. In another example, the monitoring can be based on a
rate of change of a traffic queue. In yet another example, the
monitoring can be based on subsystem states (e.g., PCI Express
going to sleep). In general, as this monitoring process effects an
upper layer control, the analysis can focus on such things as
pending work requests, tasks, protocols that provide more bandwidth
intelligence (e.g., AV bridging), etc. As noted, effecting an upper
layer control of the power consumption mode transitions removes
significant limitations of PHY-based control methods and
systems.
FIG. 4 illustrates an example switching system in which the
principles of the present invention can be implemented. In various
examples, switching system 400 can represent a router or any other
device that incorporates multi-port switch functionality. In
various example, the switch can be a consumer, SMB, enterprise,
metro, or access switch. In another example, switching system 400
can represent a voice over IP (VoIP) chip that has a network
interface (Port 0) and a PC interface (Port 1). In yet another
example, switching system 400 can represent a customer premise
equipment (CPE) device in a service provider access network that
can have an optical central office (CO) facing interface (Port 0)
and multiple interfaces (Ports 1-N) that are facing the home and/or
gateway (e.g., the CPE can simply be a media converter and/or part
of the home gateway). Still further, switching system 400 can
represent an access point such as a WLAN base station.
As illustrated, switching system 400 includes switch 410 that
supports an internal port and a plurality of external ports 0-N via
MAC and PHY interfaces. Switch 410 is also supported by buffers 420
and control 430.
In this example system, the operating system, the switch software,
control 430, and/or and/or a MAC can be designed to monitor one or
more conditions to determine whether a transition in a power
consumption mode for a PHY should be made. Similar to above, the
monitoring can relate to a buffer level relative to a watermark, a
rate of change of a traffic queue, or any other upper layer
control.
FIG. 5 illustrates a generic mechanism by which a power consumption
mode control signal can be generated. As illustrated, various upper
layer monitored parameters (e.g., queue depths, traffic classes,
pending work requests, etc.) can be used as inputs to power
consumption mode determination 510. As would be appreciated, the
principles of the present invention would not be dependent on the
particular set of upper layer monitored parameters that are used as
input. With a particular input set of upper layer monitored
parameters, power consumption mode determination 510 can then
produce a control signal for use by the PHY.
FIG. 6 illustrates a simple example of a control signal produced by
examining a transmit queue depth. In this implementation, the depth
of transmit queue 600 relative to two watermark levels can be used
to generate a control signal for the PHY. As illustrated, the
passage of the queue depth below watermark 610 would generate a
control signal that signals to the PHY to enter into a lower power
consumption mode having a lower link rate. This reduced power mode
reflects the relative lack of necessity of transmission bandwidth.
Conversely, the passage of the queue depth above watermark 620
would generate a control signal that signals to the PHY to enter
into a higher power consumption mode having a higher link rate.
This increased power mode reflects the relative necessity of
increased transmission bandwidth.
In the example of FIG. 6, it should also be noted that the rate of
change of the queue can be monitored. For example, a detection of a
rapidly filling queue could generate a control signal for the PHY
to enter a higher power consumption mode having a higher link rate,
while a detection of a rapidly emptying queue could generate a
control signal for the PHY to enter a lower power consumption mode
having a lower link rate.
In another example, a controller can be designed that would receive
multiple inputs, such as a transmission queue signal, a PCI state
signal (e.g., L states), and a pending request signal. Here, an AND
gate on all three input signals can be used to determine whether to
enter into a lower power consumption mode, while an OR gate can be
used to get out of the lower power consumption mode.
Regardless of the particular upper layer in which the control is
effected, the power consumption mode control decision is
communicated from a MAC to a PHY. It is a feature of the present
invention that this control signal would provide the PHY with
information that enables the PHY to perform a power consumption
mode switch. In one embodiment, the control signal over the MAC/PHY
interface can be used by to identify when to switch power
consumption mode, and the particular power consumption mode to
switch to. For example, the control signal can identify how much to
slow down (e.g., shut down) or speed up the link rate of the PHY.
In one embodiment, the control signal can also include information
about the operation of the interface between the PHY and MAC (e.g.,
MAC/PHY interface itself going silent). In various examples,
information regarding the parameters of how the MAC/PHY interface
emerges from a silent or sleep state (e.g., time for the clock
resync, etc.) can be communicated over the MAC/PHY interface, out
of band, and/or programmed through a packet exchange/registers.
It should be noted that the decision to slow down (or shut down)
need not happen in real time. This is in contrast to the decision
to speed up, the delay of which can lead to buffering requirements
that can become huge and unfeasible.
In the present invention, the control signal can be provided via
the MAC/PHY interface using in-band signaling (e.g., extra bits
present in an xMII interface), out-of-band signaling (e.g.,
external dedicated signaling, extra pins, etc.), or through a
packet exchange and/or register accesses (e.g., register over MDIO
and/or other methods). As would be appreciated, the particular
mechanism used to effect such control signaling would be
implementation dependent.
It should also be noted that the MAC/PHY interface can be designed
to support power consumption mode change signaling from the PHY to
the MAC. This form of reporting can be useful where symmetric
switching is implemented such that a power consumption mode switch
signaled by a far-end peer device would cause a corresponding
switch in the link-rate transmission downstream to the far-end peer
device. For asymmetric operation, the switching policy simply looks
at one direction at a time (i.e., only the transmit path). Here,
the far end side simply needs to ready itself for the change.
To further illustrate the features of the present invention,
reference is now made to the flowchart of FIG. 7. As illustrated,
the process begins at step 702 where an upper layer monitors an
operating condition. As noted, this operating condition can relate
to a buffer, queue, subsystem state, work request, bandwidth
allocation protocol, etc. Based on this monitoring, the upper layer
can determine at step 704 whether a change in link rate is needed.
If a change in link rate is not needed, then the process continues
back to step 702 where the upper layer continues to monitor the
system operating condition. If, on the other hand, the upper layer
determines that a change in link rate is needed, then the process
continues to step 706 where the control signal regarding a switch
in power consumption mode is communicated to the PHY via the
MAC/PHY interface (e.g., inband, out-of-band, etc.). In various
embodiments, the control signal can be generated by the MAC, MAC
control, MAC client, or higher layer (e.g., application layer).
Upon receipt of the control signal by the PHY over the MAC/PHY
interface, the PHY would then switch the power consumption mode at
step 708. This switch of power consumption mode can be effected in
various ways, such as through subset PHYs, low power idle modes,
etc.
The process of FIG. 7 illustrates an example of asymmetric
operation where the switching policy simply looks at one direction
at a time. For symmetric operation, the switching policy for both
directions are related. FIG. 8 illustrates an example of symmetric
operation.
As illustrated, the process begins at step 802 where the system is
operating at full capacity. At step 804, a local device detects a
power savings opportunity. Based on this detection, at step 806,
the local device then sends a request to a remote device via the
PHY to switch to a power savings state. At step 808, the link
partner response to the transmitted request is determined. If it is
determined at step 808 that the link partner has denied the
request, then the system continues to operate at full capacity. If,
on the other hand, it is determined at step 808 that the link
partner has accepted the request, then the process continues to
step 810 where the both ends of the system transition to operate in
the power savings state. As noted above, this process would be
facilitated by messaging through the MAC/PHY interface on both
ends. After the system has transitioned to the power savings state,
either device's control policy can then trigger the return to full
capacity. This process is represented by the detection at step 812,
which causes the process to return to full capacity operation at
step 802.
As has been described, a coordinated end-to-end control policy such
as that exemplified by FIG. 2 can be implemented such that power
savings can be realized by the PHYs. Significantly, this
coordinated end-to-end control policy can be implemented at one or
more higher layers of both link partners.
In one embodiment, the PHY can be configured such that it can
control switching between power consumption modes on its own. In
this configuration, the PHY can control the switching based on an
examination of multiple packets received from the MAC. FIG. 9
illustrates an embodiment of such functionality integrated into a
PHY. As illustrated, PHY 900 includes transmitter section 910 and
receiver section 920. Transmitter section 910 includes transmitter
(TX) 911, parallel-in-serial-out (PISO) block 912, encoder 913, and
transmit FIFO 914. In general, PISO 912 takes the TX code group
output from PCS encoder 913 and generates a serial output for the
PMD. The operation of PISO 912 is based on a clock signal generated
by a clock multiplier unit (CMU), which multiplies the incoming
parallel PMA TX clock. In one embodiment, PISO 912 has a single
shift register that receives the parallel data once per parallel
clock and shifts it out at the higher serial clock rate.
Receiver section 920 includes receiver (RX) 921,
serial-in-parallel-out (SIPO) block 922, clock recovery 923, PCS
decoder 924, and alignment FIFO 925. In general, SIPO 922 takes the
serial input from the PMD and generates the RX code group for the
PMA. The RX code group is processed by PCS decoder 924 in
accordance with an embedded clock in the received signal. This
recovered clock signal is generated by a clock recovery unit (CRU),
which divides the incoming clock down to the parallel rate for
output to the PCS.
As FIG. 9 further illustrates, PHY 900 also includes multi-packet
buffer 930, which buffers packets in the interface with the MAC. In
general multi-packet buffer 930 enables PHY 900 to perform its own
control of switching between power consumption modes through an
examination of multiple packets. In one embodiment, this control is
effected by control logic 940, which can examine a relative
fullness of multi-packet buffer 930. In one example, control logic
940 can be configured to monitor a fullness of multi-packet buffer
930 relative to a threshold, wherein a crossing of the threshold
would produce a switch control signal.
It is a feature of the present invention that the inclusion of a
multi-packet buffer in the PHY would enable a delay in the
transmission of packets by the PHY. This can be useful, for
example, where the PHY is in a process of transitioning from a
lower functioning state (e.g., sleep or low link rate) to a higher
functioning state. The inclusion of multi-packet buffer in the PHY
would thereby enable a transmission delay until the PHY has
effectively transitioned to the needed operating state.
Conventional PHYs do not implement any buffering and are therefore
responsible for transmitting whatever information is received from
the MAC. By inclusion of buffering in the PHY, the PHY can store,
transition (e.g., based on an increasing or absolute/threshold
fullness), and then transmit information without issue, even when
the power consumption mode was initially lowered due to upper layer
control. With the principles of the present invention, a PHY can
maintain effective operation irrespective of who controlled the
earlier transition of power consumption mode.
The inclusion of multi-packet buffering in the PHY would also
enable the PHY to make fine-grained control decisions. For example,
the PHY can determine whether the multi-packet buffer is empty or
at a low threshold, then proceed to transition the PHY to a lower
power consumption mode.
As would be appreciated, the principles of the present invention
can be applied to any type of MAC/PHY interface (e.g., internal or
external), and can use any form of signaling (e.g., in-band,
out-of-band, etc.) in effecting power consumption mode changes in
the PHY. As such, the principles of the present invention can be
applied to various PHY types (e.g., backplane, twisted pair,
optical, etc.) as well as standard or non-standard (e.g., 2.5G, 5G,
etc.) link rates, as well as future link rates (e.g., 40G, 100G,
etc.).
These and other aspects of the present invention will become
apparent to those skilled in the art by a review of the preceding
detailed description. Although a number of salient features of the
present invention have been described above, the invention is
capable of other embodiments and of being practiced and carried out
in various ways that would be apparent to one of ordinary skill in
the art after reading the disclosed invention, therefore the above
description should not be considered to be exclusive of these other
embodiments. Also, it is to be understood that the phraseology and
terminology employed herein are for the purposes of description and
should not be regarded as limiting.
* * * * *